At the start of Stephen King’s ”The Dark Tower VI: Song of Susannah,” there’s no synopsis to remind you of the backstory. ”By the time you get to Six,” says EW’s back-page columnist, referring to the second-to-last entry of his epic, ”It’s just f—ing ridiculous to try and sum up what’s gone before.” In other words, start with Book One if you’re a newbie. But for fans, ”Stephen King” not only pops up as a character in this one – he also stars in a helluva cliffhanger, which King promises will be explained in the final ”Dark Tower” book, due in September. In the meantime, he’ll be cowriting a nonfiction book with novelist Stewart O’Nan about the 2004 Boston Red Sox. And he’s also started a new novel: ”I don’t know how well it’s going, but the nice thing about it is, having announced my retirement, I don’t feel like I’m under any pressure.”